Filter cartridge assembly and method of manufacture

ABSTRACT

An apparatus for filtering well fluids and method of manufacture is disclosed. The apparatus includes an inner support, a filter helically wrapped around the inner support, and an outer support helically wrapped around the filter. The outer support frictionally engages the filter and encloses the filter between the inner and outer supports. The filter may have offset longitudinal edges which overlap. The filter may be held in place by friction with both the inner and outer supports. The method of manufacturing the apparatus includes helically wrapping a filter medium together with a metal sheet onto an inner support, the metal sheet frictionally engaging the filter medium to retain the filter medium between the metal sheet and the inner support.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 10/427,769, filed Apr. 30, 2003, entitled “FilterCartridge Assembly and Method of Manufacture” which claims the benefitof U.S. Provisional Application Ser. No. 60/393,979, filed Jul. 3, 2002,entitled “Filter Cartridge Assembly and Method of Manufacture.”

BACKGROUND

The present invention relates to the filtering of fluids, and moreparticularly to the filtering of well fluids. Still more particularly,the present invention relates to the method of manufacturing of suchfilters.

Well filters are typically used in subterranean environments in which itis desired to remove a liquid or gas from the ground without bringingsoil particulates, such as sand or clay, up with the liquid or gas. Awell filter generally includes an inner support member, such as aperforated core, and a filter body including a filter medium disposedaround the inner support member. In many cases, the well filter willfurther include an outer protective member, such as a perforated cage orshroud, disposed around the filter body for protecting it from abrasionand impacts. A filter for subterranean use is described in U.S. Pat. No.6,382,318, hereby incorporated herein by reference. A downhole screenand method of manufacture is described in U.S. Pat. No. 5,305,468,hereby incorporated herein by reference.

In order to facilitate installation of the cage over the filter body,there is usually a clearance between the outer periphery of the filterbody and the inner periphery of the outer protective member. Thisclearance between the filter body and the outer protective member orshroud is problematic. During use of the well filter in a well, fluidwill usually flow radially inwards through the filter body. However, onoccasions, such as during acidizing of a well, injection of mud into awell, air sparging, or momentary pressure reversals, fluid may flowradially outwards through the filter body, producing harmful hoopstresses which stretch the filter medium in the filter body outwardstoward the outer shroud. Because of the clearance between the filterbody and the cage, there is a likelihood of the hoop stresses exceedingthe strength of some or all portions of the filter body and producingexcessive plastic elongation of the filter medium or damage to seams orjoints of the filter body.

It is known in the art to form the outer shroud separately from thefilter body and slide it over an end of the inner support member untilit surrounds the filter body. After the shroud is disposed around thefilter body, the shroud is plastically deformed radially inwardly toreduce the inner diameter of the shroud to a value such that the filterbody can expand against the shroud. This process is also know as“swaging,” and is typically achieved using a reducing mill or die.Swaging has several drawbacks, making it an undesirable step whichshould be avoided in manufacturing well filters. First, it adds to thetime and expense of manufacturing the filter. Second, it deforms theouter shroud, putting additional stresses on the shroud and affectingits material makeup. Third, swaging does not guarantee that theclearance between the filter body and the shroud has been properlyeliminated, or that the pressure on the filter body is desirable,especially considering the “spring-back” phenomenon. Spring-back occurswhen the outer shroud expands slightly after the radial inward forceexerted by the mill or die has been released.

Other common practices in the well filter industry also cause problemsin manufacturing well filters. Often times the filter body, typically amesh screen, is hand wrapped around the inner support. However, it isnot possible to hand wrap the filter body as tight as is necessary,thereby creating unwanted slack in the filter. To combat this problem,the filter body is wrapped around the inner support longitudinally and alengthwise weld is applied at the seam. Typically, a plasma or laserweld is used at the seam so as not to burn the fine mesh. However, thisis time-consuming and expensive. Also, regardless of the type of weldused and care taken, welding causes the mesh in and around the weld todraw together, thereby causing the filter to bend and contort inundesirable ways. The weld also weakens the area around the weld and,over time, can cause erosion and breakage.

In prior art filters and methods, the filter body is usually bound tothe inner support using a variety of techniques, including chemicalglues and heat. In a process called sintering, the filter body is heatedafter it is in contact with the inner support. However, this techniquedoes not bind the filter body to the inner support properly, andadditionally plugs some of the small holes in the filter mesh andshrinks the filter body.

The industry would welcome a filter and method of manufacturing such afilter that eliminates the problems found with conventional filters andmethods. The present invention overcomes the deficiencies of the priorart.

SUMMARY

An apparatus for filtering well fluids comprises an inner support, afilter helically wrapped around the inner support, and an outer supporthelically wrapped around the filter enclosing the filter between theinner and outer supports, wherein the outer support frictionally engagesthe filter. In some embodiments, and the filter is held in place byfriction with the inner and outer supports. In other embodiments, thefilter has longitudinal edges that are offset and overlapping.

A well filter for filtering a radial flow of well fluids comprises afilter medium/metal sheet combination formed by laying a filter mediumonto a metal sheet with the filter medium being unconnected to the metalsheet, and with the filter medium being together on the metal sheet, thefilter medium/metal sheet combination being helically wrapped onto aperforated tubular member, the metal sheet frictionally engaging thefilter medium to retain the filter medium between the metal sheet andthe perforated tubular member.

The features and characteristics mentioned above, and others, providedby the various embodiments of this invention will be readily apparent tothose skilled in the art upon reading the following detaileddescription, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of a preferred embodiment of the invention,reference will now be made to the accompanying drawings wherein:

FIG. 1 is a side elevational view of an embodiment of a filter cartridgeassembly according to the present invention;

FIG. 2 is a schematic in elevational of the components of the filtercartridge assembly having been inserted into a mill to produce thefilter cartridge assembly of FIG. 1;

FIG. 3 is a side elevational view of the partially formed filtercartridge assembly of FIG. 2 without showing the mill;

FIG. 4 is a cross-sectional view of the partially formed filtercartridge assembly of FIG. 3 taken along the place A-A;

FIG. 5 is a perspective view of the partially formed filter cartridgeassembly of FIG. 3; and

FIG. 6 is a side elevational view of an alternative embodiment of apartially formed cartridge assembly having multiple layers of filtermedia; and

FIG. 7 is a longitudinal, cross-sectional view of an alternativeembodiment of the finished portion of the filter cartridge assembly ofFIG. 6, showing one half of the cartridge assembly.

NOTATION AND NOMENCLATURE

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus are to beinterpreted to mean “including, but not limited to . . . ”.

The present invention is susceptible to embodiments of different forms.There are shown in the drawings, and herein will be described in detail,specific embodiments of the present invention, including its use as afilter cartridge assembly for separating contaminants from a liquid inwhich the contaminants are suspended. This exemplary disclosure isprovided with the understanding that it is to be considered anexemplification of the principles of the invention, and is not intendedto limit the invention to that illustrated and described herein. Inparticular, various embodiments of the present invention provide anumber of different constructions and methods of operation. It is to befully recognized that the different teachings of the embodimentsdiscussed below may be employed separately or in any suitablecombination to produce desired results.

Reference to up or down will be made for purposes of description with“up,” “upward,” or “upper” meaning toward the surface of a well and“down,” “downward,” or “lower” meaning toward the bottom of a well.

DETAILED DESCRIPTION

A number of embodiments of a filter cartridge assembly according to thepresent invention will now be described with reference to theaccompanying drawings. Referring initially to FIG. 1, the filtercartridge assembly 10 is shown with perforations 12 and spiral welds 14.Referring also to FIG. 4, it can be seen that filter cartridge assembly10 includes an inner support member 20, a filter body 36 surroundinginner support member 20 and containing a filter medium 30 (seen in FIGS.2 and 3), and a restraining member in the form of an outer shroud 40surrounding filter body 36 for preventing damage to the filter medium 30in filter body 36 when filter body 36 is subjected to radially-directedforces.

Inner support member 20 provides rigidity to filter assembly 10 andserves to axially transport fluid between filter assembly 10 and anothermember to which filter assembly 10 is connected. For example, when thefilter is used for outside-in filtration, inner support member 20 cantransport filtrate (the filtered liquid) which has passed through filterbody 36 to another member, such as a pipe string, connected to innersupport member 20 for transporting the filtrate outside the well.Alternatively, filter assembly 10 may be manufactured without innersupport member 20 if the other member to which filter assembly 10 isattached, such as a pipe string, is correctly configured to receivefilter body 36 and transport the fluid filtrate to the inner portion ofthe pipe string.

Typically inner support member 20 is a hollow, tubular member and hasperforations 24, such as holes, pores, slits, or other openings of anydesired shape, in its peripheral wall which permit fluid to flow intothe central flowbore of inner support member 20. Inner support member 20need not be cylindrical as long as it is capable of transportingfiltrate. For example, it may be a solid, porous member through whichfiltrate can flow axially, or it may be a solid member having axialchannels in its outer surface for the transport of fluid. For reasons ofstrength, it is usually cylindrical, but other shapes may be employed,such as a shape with a polygonal or oval cross section, and the crosssection may vary along its length. Preferably, inner support member 20is a cylindrical steel tube having a uniform circular cross section overmost of its length and having perforations 24 for filtrate formed over aportion of its length in a region on which filter body 36 is mounted.Also, inner support member 20 is spirally wrapped and welded, resultingin spiral welds similar to welds 14 in FIG. 1. The spiral welds helpinner support member 20 withstand the pressures on filter assembly 10during use.

Inner support member 20 can be made of any material capable ofwithstanding the conditions to which inner support member 20 is to besubjected during installation and use. If inner support member 20 isexpected to be subjected to only low tensile, torsional, or radialcompressive forces, light-weight lockseam tubing or polymeric tubing maybe employed for inner support member 20. If inner support member 20 isto be used in a well for oil or gas, inner support member 20 willtypically be made from a length of spiral-welded steel tube so that itcan withstand the very high compressive forces which may be encounteredin such wells. If filter body 36 is sufficiently strong, it may bepossible to omit the inner support member 20. If the filter assembly 10is to be installed at the tail end of a pipe string or other conduit,the lower end of inner support member 20 may be closed off with a bullplug or similar member.

The length of inner support member 20 may vary according to the user'sspecifications, and almost any length may easily be accommodatedaccording to the method of the present invention, to be more fullydescribed hereinafter. After inner support member 20 has been sized andcut, the ends 26 of inner support member 20 will be generally flat andunfinished. Minimal milling, grinding, or polishing may be needed toprepare the ends 26 for welding to another member, such as a productionpipe. Alternatively, inner support member 20 may be equipped withconnecting portions at one or both ends to enable inner support member20 to be connected to other members. For example, ends 26 may bethreaded pin or box ends which can be threaded into the threaded pin orbox ends of a pipe or into a standard pipe connector for joining twopipes. However, connecting portions increase the time and expense ofmanufacturing inner support member 20 as well as the members to whichinner support member 20 is to be attached. It is preferable tomanufacture inner support member 20 so that it may be welded to othermembers.

Referring now to FIGS. 2-4, filter body 36 contains a filter medium 30which in the present embodiment is used to filter a well fluid, althoughthe filter medium may be used to filter any contaminant from any liquid,or for other fluid treatment purposes, such as for coalescing orformation of air bubbles (sparging). Filter body 36 may have anystructure capable of performing the intended removal of substances fromthe fluid being filtered or other type of fluid treatment and may employany desired type of filter medium, such as meshes, membranes, perforatedsheets or plates, wire wrap, or porous bodies comprising particlescoated and held together by a binder. Filter medium 30 will usually beone which is capable of resisting a tensile stress, as opposed to afilter medium comprising loose particles packed into an annular space.Filter medium 30 may be made of any suitable material, including but notbeing limited to metals and polymers.

In addition to some type of filter medium 30, the filter body 36 mayinclude a variety of other components, such as drainage layers to assistthe flow of the fluid into the filter medium and the flow of filtrateinto inner support member 20, cushioning layers to prevent abrasion ofthe filter medium, diffusion layers placed between layers of filtermedium to permit edgewise flow of fluid, and layers for selectivelyblocking flow through portions of filter body 36. The structure and useof these and other components of a filter body are well known to thoseskilled in the art.

Before filter medium 30 becomes incorporated into filter body 36, it istypically a flat sheet of mesh or other material from which particularsizes of sheets may be cut. A typical sheet has a width and asubstantial length rolled into a coil. Filter medium 30 is incorporatedinto the filter cartridge assembly 10 via the process describedhereinafter. Other components may be added to or around filter medium 30during this process, thereby creating the formed filter body 36 offilter assembly 10.

Referring to FIGS. 2-5, outer shroud or restraining member 40 surroundsfilter body 36. Before being incorporated into filter cartridge assembly10, shroud 40 is a flat metal sheet 46, as seen in FIG. 4. Metal sheet46 is preferably made of a material which is impervious to the fluidbeing filtered and the contaminants contained therein. Therefore, outershroud 40 is preferably made of stainless steel. Sheet 46 is also formedwith perforations 12, such as holes, pores, slits, or other openings ofany desired shape, through which the fluids to be filtered can flow toreach and flow through the filter body 36.

Outer shroud 40 serves a variety of functions. One function is toprotect filter body 36 against erosion, abrasion, and impacts, eitherduring installation or operation of filter assembly 10 underground.Another function is that of a restraining member which restrains filterbody 36 against radial expansion due to radially outward forces actingon filter body 36 so as to limit the elongation (expressed as strain) offilter body 36. Filter body 36 has a maximum allowable elongationdefined as the highest elongation at which filter body 36 can stillremove particles of a given size with a desired efficiency. Preferably,restraining member 40 limits the elongation of filter body 36 to lessthan the maximum allowable elongation by a safety factor. In addition torestraining filter body 36, outer shroud 40 must exert enough radiallyinward force on filter body 36 so as to create a frictional engagementor bind between shroud 40 and filter body 36, and between inner supportmember 20 and filter body 36. Preferably, filter body 36 is insubstantial contact with but not connected to inner support member 20 orshroud 40.

The frictional engagement or bind between the inner and outer surfacesof filter body 36 and inner support member 20 and outer shroud 40,respectively, is required for several reasons. First, preferably, filterassembly 10 has no connecting portions at its ends connecting innersupport member 20, filter body 36, and outer shroud 40. Thus thefrictional bind holds the separate pieces together without connectingmeans on the ends 16 of filter assembly 10. Second, it is beneficial forfilter body 36 to resist movement in the lengthwise direction of filterassembly 10 in response to axial forces. Lastly, frictional engagementwill tend to prevent fluid from bypassing filter body 36 by flowingbetween filter body 36 and inner support member 20 or outer shroud 40.

Referring now to FIGS. 2-5, the process of manufacturing filtercartridge assembly 10 generally includes simultaneously wrapping filtermedia 30 and metal sheet 46 for outer shroud 40 around inner supportmember 20 in a spiral or helical fashion so as to dispose filter media30 between inner support member 20 and outer shroud 40 once shroud 40has been formed and welded from metal sheet 46. As metal sheet 46 isspirally wrapped around inner support member 20, it is automaticallywelded at seams 14. Filter media 30 is overlapped but not welded. Thus,only outer shroud 40 is being welded, and not filter body 36.

Referring to FIG. 2, a pre-formed perforated tube is used as innersupport member 20, and is fed into a mill 50 in the direction of arrow22. As described above, the pre-formed inner support member 20 ispreferably spirally wrapped and welded to provide flexibility andstrength in response to the pressures encountered by filter assembly 10during installation and use. As one of the ends 26 of inner supportmember 20 continues to be fed into mill 50, mill 50 engages innersupport member 20 and continues to move support member 20 in thedirection of arrow 22. At the moment of engagement, referring now toFIGS. 3 and 5, mill 50 begins to rotate support member 20 in thedirection of arrow 42 around longitudinal axis 48.

Referring now to FIGS. 2-5, subsequent to the engagement of supportmember 20 by mill 50, a combination of filter medium 30 and perforatedmetal sheet 46 are fed into mill 50 according to arrow 32, as seen inFIG. 2. In FIGS. 4 and 5, it can be seen that filter medium 30 is a flatsheet or layer of wire mesh having a predetermined width, or any of thevarious materials that filter medium 30 may be comprised of, laid overthe top of metal sheet 46, which may comprise any of the variousmaterials that outer shroud 40 may be made of. It should be understoodthat multiple layers of filter medium 30 may be laid over the top ofmetal sheet 46 at one time. In FIGS. 2 and 3, the width w of filtermedium 30 may be the same as the width of sheet 46, or it may be smalleror larger. In a preferred embodiment, a plurality of layers of filtermedia 30 is used wherein the width of each layer is no larger than thewidth of sheet 46. Also, each layer is staggered or offset laterallyfrom the layer above and/or below it so that the edges of the multiplelayers do not align. Consequently, when metal sheet 46 and filter media30 are spirally wrapped, a mechanical seal is created within the filterbody 36, which will be more fully described hereinbelow.

Mill 50 also engages filter sheet 30 and metal sheet 46, and continuesto move them in the direction of arrow 32. Referring now to FIGS. 3-5,the spiral wrapping process is illustrated. As sheets 30 and 46 comeinto contact with inner support member 20, mill 50 forms metal sheet 46into outer shroud 40, thereby also shaping filter sheet 30 into filterbody 36. FIG. 4 illustrates a cross section of the forming process, witharrow 32 showing the movement of filter medium sheet 30 laid over thetop of metal sheet 46. At location 38, the mill (not shown) forms sheet46 into outer shroud 40 by cold-rolling the metal or other material,thereby forming and trapping filter body 36 between inner support member20 and outer shroud 40. Arrow 42 represents the rotational movement ofinner support member 20, filter body 36, and outer shroud 40, which allcombine to form filter cartridge assembly 10. It should be noted thatrotational movement 42 may be clockwise or counter-clockwise dependingon the spiral mill orientation.

The simultaneous advancement and rotation of inner support member 20through mill 50 as sheet 30 and sheet 46 are cold-rolled around supportmember 20 creates the spiraling of outer shroud 40. If necessary, sheets30 and 46 may be fed into mill 50 at an angle in relation tolongitudinal axis 48, rather than at a right angle as seen in FIG. 3, toenhance the spiral wrapping process. Sheets 30 and 46 may be advancedinto mill 50 at a prescribed angle, the angle depending on the outerdiameter of inner support member 20 and the width of sheet 46.

Preferably each wrap of outer shroud 40 is flush with the immediatelypreceding wrap, thereby forming seams 14 as seen in FIGS. 2, 3, and 5.As each new wrap of cold-rolled outer shroud 40 is formed flush with theimmediately preceding wrap, mill 50 automatically welds the outer shroud40 at seams 14. The weld may be any of the various types of welds knowin the art, although a fusion-type weld is preferred. It is notnecessary to weld filter body 36 once outer shroud 40 has been welded.

As mentioned hereinbefore, frictional engagements or binds hold filtercartridge assembly 10 together once the forming and welding processeshave been completed. To ensure frictional engagement, several steps aretaken. First, the thickness or gage of filter medium 30 is determined.This measurement is usually determined according to the application towhich filter assembly 10 is to be put and the contaminant which filterassembly 10 is intended to filter. Next, the optimal outside diameter ofthe finished cartridge assembly 10 is determined. Finally, a formula isused to determine the inside diameter of outer shroud 40 required toenclose the filter body 36 properly around support member 20. Thus, thevariable dimension for achieving the proper frictional engagement is theinside diameter of outer shroud 40.

Filter cartridge assembly 10 must be able to filter very small particlesfrom the fluid being passed through it. For example, the filtrationcapabilities of filter assembly 10 may be, but is not limited to, 200microns. To ensure that no particle greater than 200 microns passesthrough filter assembly 10, a mechanical seal must be achieved at theseams of the wrapped filter body 36. One way to achieve such seals is toextend the width of filter medium 30 at the leading edge 43, seen inFIGS. 2, 3 and 5. As each new spiral wrap is formed, the exposed leadingedge 43 of partially formed filter assembly 10 includes an exposed layerof filter body 36. This exposed layer of filter body 36 is overlapped bythe filter body of the trailing edge 45 as trailing edge 45 lays flushwith the exposed portion of outer shroud 40 from the previous wrap.Filter body 36 is sealed by pressure from the cold-rolled wrappingprocess through the creation of a double dense filter body at theoverlapping intervals.

The overlapping intervals may be any predetermined width, and they mayvary along the length of filter assembly 10. For illustrative purposes,the overlapping intervals may be 2 to 6 inches wide, or greater or less,depending partially upon the width of metal sheet 46. Sheet 46 may, forexample, be 5 inches wide, with the overlapping intervals being in therange of 1 to 2.5 inches, or possibly less.

Referring now to FIG. 6, an alternative embodiment to the filtercartridge assembly thus far described is shown. Filter cartridgeassembly 50 is shown having the same inner support 20 and metal sheet 46which is formed into outer shroud 40 with welds 14. However, the filterbody of cartridge 50 is made up of multiple layers of filter media 52,54. Before metal sheet 46 and layers 52, 54 are spirally wrapped, layer52 is placed on top of metal sheet 46, typically offset from thetrailing edge 45 of metal sheet 46 as shown in FIG. 6. This offset oflayer 52 helps prevent layer 52 from being damaged by the welding atseams 14. Then, layer 54 is placed on top of layer 52, staggered oroffset in the manner shown in FIG. 6. Upon the completion of each spiralwrap, a wrapped portion 54 a of layer 54 remains exposed. Portion 54 ais then wrapped over by layer 52 upon completion of the next spiralwrap, with trailing edge 54 b of the new wrapped layer 54 substantiallyaligning with the leading edge 54 c of the previously wrapped layer 54.Typically, the widths of each of layers 52, 54 will be less than thewidth of metal sheet 46, although the total width of the offset layers52, 54 will be greater than the width of metal sheet 46. Also, thealigned edges 54 b and 54 c of the completed portion of cartridge 50will usually not be perfectly flush, thereby creating gaps betweenaligned layers of filter media. These gaps are shown and described belowwith reference to FIG. 7.

Referring to FIG. 7, a cross-sectional portion of a completed filtercartridge assembly is shown depicting an alternative to the embodimentshown in FIG. 6. The longitudinal portion 60 of a finished cartridgeassembly shows the inner support 20 and outer shroud 40 surroundingmultiple layers 52, 54, 56, 58 of filter media. Cartridge 60 has fourlayers of filter media instead of just two, as shown in FIG. 6, althoughthe number of layers may vary depending on the desired specifications.Support 20, shroud 40, and the layers 52, 54, 56, 58 are formed in thesame way as shown in FIG. 6, with each filter media layer being offsetor staggered from each preceding layer and/or subsequent layer of filtermedia when positioned on top of metal sheet 46 before spiral wrappinghas occurred. Upon completion of the spiral wrapping process, the newlayers of filter media are wrapped over the exposed, previously wrappedlayers of filter media to form the completed layers as shown in FIG. 7.The aligned edges of the filter media layers typically do not sitperfectly flush, causing gaps to be formed at the edges, such as gaps 52a, b. However, a desirable mechanical seal is formed between the innersupport 20 and outer shroud 40 because the gaps are not radiallyaligned. For example, because the filter layers 52, 54, 56, 58 areoffset from each other before being wrapped, the gaps 52 a, b are notradially aligned with the gap 54 a. Likewise, gap 54 a is not alignedwith gap 56 a, and gap 56 a is not aligned with gaps 58 a, b as shown inFIG. 7. Each of the filter layers overlaps any gap formed between edgesof adjacent layers. Upon completion of the wrapping process, the outerfilter layer 52 will be in full mechanical contact with the innersurface of outer shroud 40, as will the inner filter layer 58 be in fullmechanical contact with the outer surface of inner support 20. This isalso typical of the previously described embodiments.

As was previously described, the width of each individual layer offilter media is preferably less than the width of metal sheet 46. Wheneach layer becomes wider than metal sheet 46, and as more layers offilter media are added, the overlapping filter layers begin to interferewith each other as wrapping continues, and the outer shroud of thecartridge assembly loses its uniform shape. To maintain a desired,uniform outer shroud shape, the widths of the filter layers should beless than the width of metal sheet 46. By doing this, multiple layers offilter media can be incorporated into the spiral wrapping processwithout filter layer interference and subsequent mis-shaping of theouter shroud.

The multiple layers of filter media of the several embodiments thus fardescribed may have different filter mesh capacities. The exact filtermesh capacities of each layer within a single cartridge assembly will bedetermined by customer specifications. However, it should be understoodthat the mesh capacities of different layers of filter media within asingle cartridge assembly may very from very coarse to very fine. Forexample, the cartridge assembly could contain two coarse layers offilter media, one in contact with the inner support and one in contactwith the outer shroud, and two fine layers disposed between the twocoarse layers. Such a cartridge assembly would contain 4 layers offilter media, although the number of layers may vary.

In an alternative embodiment, filter cartridge assembly 10 is producedwithout inner support member 20. Inner support member 20 is not neededto form cartridge assembly 10. However, without inner support member 20,it is possible that filter body 36 could separate from outer shroud 40since it is not welded in any fashion or connected to outer shroud 40.Also, filter body 36 could collapse without the inner support providedby support member 20. However, this alternative embodiment is beneficialif the production pipe to which the filter assembly is to be attachedwould provide the inner support needed, and the filter assembly would beinstalled before any outside stimulus would cause filter body 36 toseparate from outer shroud 40.

In the preferred embodiment, the finished cartridge assembly 10 is not astand-alone cartridge, meaning that the assembly 10 must be attached toa base pipe to operate properly. Mainly, this is because the ends 16 ofassembly 10 in FIG. 1 are left unfinished, thereby exposing filter body36, which is held in place by the friction binds. As mentioned earlier,this configuration eliminates the time and expense needed to connect theends 16. This configuration also eliminates the need for end portionsthat would enable assembly 10 to be connected to a base pipe, such asadditional connectors or threaded pin ends. With the currentconfiguration, the ends would simply be welded together when the userwelds the assembly 10 to a base pipe. Welding serves to both attachassembly 10 to the base pipe and close off and seal the ends 16 ofassembly 10, which is much easier and less expensive than manufacturingconnecting means. However, the filter assembly 10 may include connectorsor threaded pin or box ends to connect to a base pipe as desired.

Cartridge assembly 10, whether formed with or without inner supportmember 20, may be placed over a base pipe, then welded to the base pipeto create a finished cartridge. Alternatively, the assembly 10 may bespirally wrapped, as previously described, around a base pipe.Preferably, the inner support member is wrapped around the base pipefirst and then welded at the seams, followed by the spiral wrapping ofthe filter and outer shroud. The inner support member, filter, and outershroud components may be spirally wrapped substantially simultaneouslyaround the base pipe, although this would tend to make welding of theinner support member undesirably difficult.

Because the method of the present invention uses a continuous spiralwrapping process, the operator is able to continuously produce thefilter cartridge assembly through the mill, and stop the mill and cutthe cartridge assembly at any length desired. This creates greatflexibility in manufacturing the filter assembly 10 since the assemblymay be cut at any length as no pre-determined parameter of the spiralwrapping process causes the final length of the filter assembly 10 toalso be pre-determined.

A primary advantage of one embodiment of the present invention is theability to achieve frictional engagement between the filter and theinner support and between the filter and the outer support. A frictionalbind eliminates the need for welding and sintering of the filter body,thereby avoiding the problems previously described.

Another advantage of an embodiment of the present invention is theelimination of a swaging step to reduce the diameter of the outershroud. The simultaneous and continuous cold-rolled wrapping of theouter shroud and filter body makes the additional step of swagingunnecessary, thereby also avoiding the previously described problemswith swaging.

Other advantages include the previously described flexibility inmanufacturing different lengths of filter cartridges, and having afilter cartridge with a spirally wrapped filter body. A spirally wrappedfilter body is stronger and more flexible than a longitudinally wrappedfilter body. A spirally wrapped filter body bends more easily while alongitudinally wrapped filter body tends to kink. These samecharacteristics apply to spirally wrapped inner and outer supports.Moreover, a spirally wrapped filter body has increased filtrationversatility as the filtration capability of the filter may be adjustedby changing the overlapping intervals of the filter layers.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. While the preferredembodiment of the invention and its method of use have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not limiting.Many variations and modifications of the invention and apparatus andmethods disclosed herein are possible and are within the scope of theinvention. Accordingly, the scope of protection is not limited by thedescription set out above, but is only limited by the claims whichfollow, that scope including all equivalents of the subject matter ofthe claims.

1. An apparatus for filtering well fluids, the apparatus comprising: aninner support; a filter helically wrapped around the inner support; anouter support helically wrapped around the filter enclosing the filterbetween the inner and outer supports; wherein the outer supportfrictionally engages the filter.
 2. The apparatus of claim 1 wherein theouter support is cold-rolled over the filter.
 3. The apparatus of claim1 wherein the filter has longitudinal edges which overlap.
 4. Theapparatus of claim 3 wherein the overlapping edges are frictionallyengaged holding the edges in place.
 5. The apparatus of claim 3 whereinthe overlapping edges are not welded.
 6. The apparatus of claim 3wherein the filter comprises a plurality of layers.
 7. The apparatus ofclaim 6 wherein each of the plurality of layers is offset from the otherlayers such that the overlapping longitudinal edges do not align.
 8. Theapparatus of claim 6 wherein at least one of the filter layers includesa plurality of filter sheets.
 9. The apparatus of claim 8 wherein a seamexists between two adjoining filter sheets within a filter layer, andthe seam is substantially offset from the seams in either of theadjacent filter layers.
 10. The apparatus of claim 8 wherein a gapexists between two adjoining filter sheets within a filter layer, andthe gap is substantially offset from gaps in either of the adjacentfilter layers.
 11. The apparatus of claim 1 wherein the filter isstabilized and held in place by frictionally engaging the inner andouter supports.
 12. The apparatus of claim 1 wherein the outer supportedges are welded.
 13. The apparatus of claim 1 wherein inner and outersupports with filter therebetween are placed over a base pipe and thenwelded to the base pipe to create a cartridge.
 14. The apparatus ofclaim 13 wherein the cartridge has ends which are left unfinished. 15.The apparatus of claim 13 wherein the cartridge is cut to apredetermined length.
 16. The apparatus of claim 1 comprising a tubularwell filter cartridge, the tubular well filter cartridge having apre-determined outer diameter wherein the outer support is helicallywrapped around the filter to the pre-determined outer diameter with theouter support frictionally engaging the filter and enclosing the filterbetween the inner and outer supports.
 17. The apparatus of claim 1 forfiltering well fluids, the inner and outer supports and filter beingpermeable to the well fluids.
 18. An apparatus for filtering wellfluids, the apparatus comprising: an inner support; a filter helicallywrapped around the inner support; and an outer support helically wrappedaround the filter enclosing the filter between the inner and outersupports; wherein each helical wrap of the filter includes a pluralityof filter layers, each layer being offset from and overlapping anadjacent layer.
 19. A well filter for filtering a radial flow of wellfluids, the apparatus comprising: a filter medium/metal sheetcombination formed by laying a filter medium onto a metal sheet with thefilter medium being unconnected to the metal sheet; and with the filtermedium being together on the metal sheet, the filter medium/metal sheetcombination being helically wrapped onto a perforated tubular member;the metal sheet frictionally engaging the filter medium to retain thefilter medium between the metal sheet and the perforated tubular member.